Originally Posted by TerraNova
So just to be clear, you are saying that using a smaller, longer inner tube can create enough turbulence? Or are you saying to size down the outer tubing of the CFC to create turbulence of the coolant?
Sorry to be so thick headed I just want to understand the concept you are describing so I can build the best possible apparatus.
Thanks in advance.
Nothing wrong with asking, as this is fairly counter-intuitive, like many things.
A benefit of convolutions is to provide turbulence/mixing vs. laminar flow (it also provides minor benefit of a bit higher surface area/cross section ratio- circular tube is perfectly minimized in this regard). The turbulence of both the inner and outer liquid is important. The outer liquid, in this case, is not (usually) constrained to some maximum flow, so getting turbulence there is not (usually) an issue. The inner liquid may be flow constrained by the desired output temp (for single pass cooling). If this flow is insufficient to create turbulence, a smaller diameter tube that provides turbulence at that flow can perform better than the larger non-turbulent flow tube. It may even work at the same length, but the length may also need to be increased to meet the desired temp. That's the theory anyway. There are too many scenarios to describe when larger non-turb beats smaller turb, or vice-versa. I am just giving the rationale behind convoluted tubing, and the alternatives.
The amount of flow to get turbulence isn't that high, especially for circular spirals. I don't have any guidance to provide regarding optimal tubing size, but there have been threads on in it. Or, if you are good at math, there are the Reynolds equations to make some theoretical calcs.
The whole CFC/PC fascination is kind of lost on me, though, especially when recircing to the kettle and/or prechilling is required. I always saw them as only well suited to cases where tap water was cold enough to provide single pass cooling to ferm temps, and you either had a conical, or didn't care about all the cold break getting in your fermenter. Personally, I am an IC believer. Ease of use and simplicity trumps optimized performance in my world.